Interaction between neurophysiological studies and engineering systems approaches have been extremely successful in elevating the oculomotor system to the brain's best understood neural system. This, in turn, has had impressive clinical fall out leading to increasingly successful interpretations of the pathophysiology of eye movement disorders. However, considerable evidence has now accumulated suggesting that the eye movement control system, which to date has been almost exclusively studied in animals whose heads are restrained, is but a special case of a more general gaze control system that controls displacements of the visual axis when the head is unrestrained. The basic hypothesis underlying the proposed research is that knowledge of gaze control mechanisms will require modifications to current oculomotor system circuit diagrams and therefore that studies in the alert head-free animal are important complementary contributions to current extensive research in the head-fixed animal. The broad-term objective of my research is to provide knowledge on this gaze control system. More specifically, it is to understand the neural mechanisms that transform visual information into motor commands that move, in a coordinated manner, the eyes and head such that the visual axis acquires a visual target. In the proposed study it is planned to concentrate on determining how some brainstem neurons, classically implicated in oculomotor circuitry (omni-pause neurons, OPNs), inhibitory bursts neurons, excitatory burst neurons), are implicated in controlling gaze. (We have preliminary evidence that in head-free cats, OPNs pause not for eye saccades but for gaze saccades). The cat's gaze control system is identical in structure to that of humans. This provides an excellent and convenient animal model of the system. In the proposed experiments we will record from these brainstem neurons in cats whose heads are free to move and who are trained to orient to visual targets. Various discharge characteristics - such as burst or pause timings, duration, etc. - will be correlated to characteristics of eye, head and gaze movement trajectories in both the head-fixed and head-free behavioral conditions. In addition, to provide information on signals that drive these neurons, the burst/pause characteristics will be analyzed in conditions where head motion is perturbed mechanically.